1. Field of the Invention
This invention relates to a metal ring for an optical element, a method for fabrication of an optical element having a metal ring, and an optical element having a metal ring, and more particularly relates to a metal ring for an optical element, a method for fabrication of an optical element having a metal ring, and an optical element having a meal ring that are applied to an optical element having optical surfaces on both sides and provided with a peripheral side surface formed as the circumference of the optical element which is to be positioned on a mounting member.
2. Description of the Related Art
It has been proposed to use a V-groove 60 in which an aspherical lets 70 formed of optical glass having a small diameter of, for example, 1 mm as the conventional optical element as shown in FIG. 6, FIG. 7, and FIG. 8. The lens 70 is disposed in the V-groove 64 of a mounting base 62 disposed on a pedestal 61 so as to face to a laser diode 63 mounted on the pedestal 61 provided in a part. In the case of the structure described hereinabove, an optical axis OD of the laser diode 63 can be brought into coincidence with the optical axis of a lens OL easily only by placing and fixing the lens 70 in the V-groove 64 of the mounting base 62 as long as the dimensional precision of the peripheral surface 71 of the lens 70 is maintained precisely, and the adjustment of optical axis is not necessary.
When the abovementioned lens mounting structure is employed, the lens 70 and the mounting base 62 having the V-groove 64 are fixed together with adhesive. However, because handling of adhesive 80 is troublesome and some component evaporated from the adhesive 80 deteriorates the atmosphere around the lens when the adhesive 80 is used for fixing the lens 70, it is desired that the lens is fixed on the mounting base by means of soldering without using adhesive.
To employ soldering for fixing the lens, it is necessary that the peripheral edge of the lens should be metalized. However, if the peripheral edge of a glass lens having a small diameter as described hereinabove is metalized by means of spattering technique, it is difficult to control spattering due to such a small diameter of the lens, and it is necessary to protect the optical functional surface of the lens from being metalized. As the result, it has not been realized to manufacture the desired lens efficiently.
To solve the abovementioned problem, it has been proposed that a thin-wall ring-shaped metal ring member that is solderable is provided on the periphery of a lens.
Such a lens is formed by means of a method in which a glass lens is formed in a metal ring formed of a solderable metal thin-wall. A lens as described hereinabove is formed according to a procedure as described hereunder.
In detail, when an optical element is fabricated by use of a body die for defining the outside configuration and a force plunger for molding a desired optical functional surface by pressing both the incident surface and out-going surface of an optical material charged in the body die in an electromagnetic induction furnace, a metal ring is fixed on the periphery of the lens simultaneously.
In this example, a metal ring having an outside diameter slightly smaller than the inside diameter of the body die is inserted in the body die, an optical glass pellet that is served as the optical material is disposed in the metal ring, the body die is heated with an induction current by use of a coil provided on the outside of the body die so that the optical material is heated to a desired temperature for softening, the optical material is pressed by use of the die in the metal ring to thereby form an optical functional surface having a desired configuration. At that time, simultaneously the metal ring is pressed toward the body die disposed on the outside periphery to enlarge the diameter of the metal ring by means of the pressure applied on the optical material, and these components are cooled to obtain an optical element with a metal ring having a desired outside diameter.
According to the method for fabrication of a lens as described hereinabove, a thin-wall metal ring is disposed on the peripheral edge of a lens and the outside configuration of the metal ring disposed on the peripheral edge of the lens is formed precisely.
In other words, according to the above-mentioned fabrication method, a metal ring disposed on the periphery of the optical material is pressed outward so that the outside diameter is expanded and the metal ring is pressed onto the inside configuration of the body die disposed outside of the metal ring when the optical material disposed in the metal ring is compressed by means of a force plunger, and the optical material is solidified so as to maintain the configuration. As the result, a lens having a desired configuration can be obtained. Because thermal shrinkage of the optical material and metal ring due to cooling can be estimated, a lens having a desired configuration can be obtained by adjusting the dimension of the die previously.
However, if the optical glass is heated in contact with the die material when the optical material is heated, some component in the optical material acts upon the die material due to the heat to cause deterioration of the die material.
To avoid the abovementioned problem, a method has been proposed in which a metal ring having the periphery, which has an aperture formed on the lower end of the metal ring, bent toward inside is used so that the optical material disposed in the metal ring is not in contact with the die material during heating before pressurization.
However, according to the above-mentioned conventional technique, a metal ring is expanded not evenly when the optical material is compressed for forming by use of a die material, which is a problem.
The reason why the problem is caused is that the bent-formed portion for preventing contact formed on the one aperture periphery of the metal ring is less deformable than the other portion, and the metal ring is expanded not evenly.
As the result, a lens having the precise outside peripheral configuration cannot be obtained, and the lens cannot be disposed at a desired position when the lens is fixed on the mounting parts.